OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. Abstract SPS-produced ␣-alumina samples are prepared from powders doped with different amounts of Zr 4+ and La 3+ cations. Zr 4+ cations segregate at grain boundaries. m-ZrO 2 particles are formed at 570 but not at 280 cat ppm. A ␤-alumina LaAl 11 O 18 structure is found at 310 cat ppm when the lanthanum grain boundary solubility limit is exceeded (∼200 cat ppm). 100 cat ppm La is sufficient to block the diffusion path across grain boundaries and inhibit grain growth. Both doping cations disturb the grain boundary diffusion whatever their amount. They delay the densification at higher temperatures while limiting grain growth. The real in-line transmittance (RIT) of ␣-alumina is improved due to the reduced grain size. Nevertheless, increasing the cation amount leads to an increase in porosity or even the formation of secondary phase particles, both detrimental for optical properties. Finally, optimised amounts of cation of 200 and 150 cat ppm are found for La-and Zr-doped alumina, respectively.

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Dielectric approaches for estimating microwave heating of ceramics and polymers assuming that resistive effects are small enough to be neglected have been applied quite often. However, these approaches are not valid for semiconductors. Permittivity and resistivity are very sensitive to chemical composition; therefore it is difficult to extrapolate properties from similar materials as can be done with thermal properties. The objective of this work is to estimate the dielectric and resistive contributions during microwave heating, solving the electromagnetic and heat transfer equations by means of Finite Element Method (FEM) using the software ANSYS TM . The experiments were performed over a parallelepiped made of compacted and sintered powders of the manganite, which is a negative thermal coefficient thermistor, placed inside a waveguide and exposed to 2.45 GHz microwaves at different powers. Temperature was taken with sheathed thermocouples that also served as electrodes for monitoring electric resistance. Matching experimental data and simulation results provided values for the properties within acceptable range. An operative model for simulating heating of a sample placed in a waveguide was built, considering either resistive or dielectric effects, which in turn helps to estimate these properties applying it jointly with the experimental technique shown.

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